COAL COMBUSTION BY-PRODUCTS
DISPOSAL PRACTICES AT A SURFACE COAL
MINE IN NEW MEXICO: LEACHATE &
GROUNDWATER STUDY
June 5, 2013
ASMR Presentation
Ryan Webb
Cheryl Parker, Kara Hart, Bruce Thomson, John Stormont, Mark Stone
1
BACKGROUND
• San Juan Power Generating Station/San Juan Mine (SJM)
• Coal is mined from the Fruitland Formation and disposed of at this location
• 2.7 million tons of CCBs disposed of in landfills each year
• 70% fly ash, 20% bottom ash, 10% FGD gypsum
2
BACKGROUND
3
GOALS
• What hazardous constituents are associated with CCBs and what is their
potential for leaching from buried wastes?
• What are the geotechnical and hydraulic properties of the CCBs and how do
they affect possible infiltration of ground water through the buried waste?
• What is the rate of infiltration through the disposed CCBs?
• Are there identifiable geochemical processes occurring that affect leachate
quality or the hydraulic properties of the buried waste?
4
OBJECTIVES
• Results of leaching tests to characterize contaminant release from fresh and
buried CCBs under saturated and unsaturated conditions
• Summary of the physical properties of soils and CCBs that govern the
unsaturated flow of water through them
• Results of a one-dimensional unsaturated water flow model that estimates
infiltration of water through disposed CCB materials.
5
METHODS
• Physical Properties of CCBs
• 1-D Model Development from Lab Results
• Leach Tests
• Geochemical Characterization
• Column Tests
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METHODS
(PHYSICAL PROPERTIES)
• Grain size distribution
• Specific Gravity
• Moisture Content
• Density
• Saturated Hydraulic Conductivity
• Moisture Characteristic Curves
7
METHODS
(MODELING)
• HYDRUS 1D
• 33 m of buried CCBs (FGD not included)
• 10 years of available daily climate data
8
METHODS
(LEACH TESTS)
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METHODS
(GEOCHEMICAL CHARACTERIZATION)
• Scanning Electron Microscopy
• X-Ray Diffraction
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METHODS
(GEOCHEMICAL CHARACTERIZATION)
• Unsaturated flow columns (30 days)
• No. 8 coal seam water (2 columns) & DI water (6 columns)
• One pore volume per day
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RESULTS
(PHYSICAL CHARACTERISTICS)
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RESULTS
(PHYSICAL CHARACTERISTICS)
Property
Fly Ash
Bottom
Ash
% finer #200 sieve (0.075 mm)
% larger #200 sieve (0.075 mm)
Minimum Relative Density (kg/m3)
Maximum Relative Density (kg/m3)
Average Specific Gravity
85.4
14.6
1007.4
1184.4
2.00
22.3
77.7
692.2
813.8
2.06
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RESULTS
(PHYSICAL CHARACTERISTICS)
Material
Fly Ash
Fly Ash
Fly Ash
Bottom Ash
Bottom Ash
Bottom Ash
Top Soil
Target Dry
Density
(kg/m3)
1028.4
1113.3
1169.3
727.2
800.9
913.1
Actual Dry
Density
(kg/m3)
1024.0
1108.2
1163.0
724.4
796.9
910.4
1680.0
Sample 1 KSAT
(cm/s)
Sample 2 KSAT
(cm/s)
7.81E-05
6.62E-05
5.45E-05
3.53E-03
2.27E-03
1.48E-03
8.45E-06
1.30E-04
8.10E-05
5.96E-05
6.45E-03
6.26E-03
3.90E-03
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RESULTS
(PHYSICAL CHARACTERISTICS)
Material
Fly Ash
Fly Ash
Fly Ash
Bottom Ash
Bottom Ash
Bottom Ash
Top Soil
Pictured
Cliffs
Target Dry
Density
(kg/m3)
1028.4
1113.3
1169.3
727.2
800.9
913.1
r
(cm3/cm3)
0.003
0.00
0.00
0.00
0.00
0.00
0.202
s
(cm3/cm3)
0.55
0.52
0.47
0.56
0.66
0.63
0.44
α
(1/cm)
3.9E-03
2.4E-03
1.1E-03
4.1E-02
4.3E-02
2.5E-02
3.23E-02
1.68
1.66
1.85
1.46
1.52
1.54
0.73
0.00
0.26
5.62E-03
0.21
n
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RESULTS
(1D MODEL)
• Water flux through the top soil predicted to be virtually zero
Profile
Range of
Calculated
Point Fluxes
(cm/day)
FA only
BA only
Baseline profile
-0.02 - 0.09
0.0 - 0.12
-0.03 - 0.02
Range of
Calculated
Water
Contents
(cm/cm)
0.01 - 0.33
0.01 - 0.27
0.08 - 0.32
Range of
Observed
Water
Contents
(cm/cm)
0.16 - 0.33
0.19 - 0.27
0.08 - 0.32
16
RESULTS
(1D MODEL)
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RESULTS
(LEACH TESTS)
• High concentrations of Al, Ba, Ca, Fe, Si, and Na
• High amounts of Ba may be due to water being added for CCB transport
• As concentration roughly twice as high in fly ash
• Samples deeper in landfill show increasing concentration of Ba and possibly
B
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RESULTS
19
RESULTS
(COLUMN TESTS)
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RESULTS
(COLUMN TESTS)
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DISCUSSION
(COLUMN TESTS)
• Concentrations depend largely upon water characteristics
• Expected leaching is similar to No. 8 Coal Seam Water
• Column tests are HIGHLY accelerated (1 pore volume/day)
• Actual flow is expected to be much less
22
RESULTS
(GEOCHEMICAL ANALYSIS)
• SEM – fly ash particles are small spheres of mostly Si, Al, and O
• Bottom ash “rougher” particles and higher amounts of carbon
23
RESULTS
(GEOCHEMICAL ANALYSIS)
• Deepest cores show significant degradation
24
RESULTS
(X-RAY DIFFRACTION)
• Fresh bottom ash – suggests mullite and quartz are dominant
• Amorphous peak less distinctive as in fly ash samples
• Two peaks consistent with the presence of Calcite and Feldspar
• Patterns display aging from a glassy amorphous phase to a more
clay/crystalline structure
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DISCUSSION
• Column tests show highly accelerated rates and DI water is a much more
aggressive leaching solution than ground water.
• B, Ca, Mo, and Sr will likely follow decreasing trend quickly
• Flow may be either unsaturated water or groundwater in aquifer, depending
on future water table levels
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DISCUSSION
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CONCLUSION
• No evidence of groundwater contamination from CCB disposal has been
found
• Element concentrations may be higher than native groundwater, although
mostly of the same order of magnitude
• Little to zero vertical flux through cover materials is expected
• The potential for contamination of the underlying regional aquifer at the
SJCM is small
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ACKNOWLEDEMENTS
• bhp Billiton
• PNM
• NMMMD
• Advisory committee
• DBS&A
• Undergraduate laboratory assistance
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QUESTIONS?
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